The tumor suppressor gene TP53 sits at the crux of response to cellular stresses. This is the most frequently inactivated gene in human tumors, being the target of somatic mutations. The protein product of TP53 is p53, and plays a crucial role in anti-proliferative signals through the induction of apoptosis, senescence, and cell-cycle arrest when activated by stresses such as genotoxic chemotherapeutic drugs. Therefore, the status of TP53 mutation in a tumor has profound implications for the tumorigenic potential as well as the response to anti-cancer therapies. Indeed, numerous studies have shown a predictive and prognostic value of TP53 mutations to the response to chemotherapy, but just as many studies show no significant contribution of TP53 mutations to chemotherapy response. This controversy is partly due to the lack of standard methods of TP53 mutation detection, but more importantly, it is due to the categorization of all TP53 mutations into one group. Certain mutations in TP53 can confer a mutant p53 with new, gained activities, not normally present in the WT p53 protein. These have been commonly called "gain of function" (GOF) p53 proteins, and some GOF p53 proteins can even confer oncogenic properties. However, not all gained functions are necessarily implicated in oncogenicity. Using stringent criteria, we have defined a select group of GOF TP53 mutations that do function as oncogenic proteins as oncomorphic TP53 mutations. In this work, we utilize data available from a large patient population through The Cancer Genome Atlas (TCGA) as well as data available from the University of Iowa Gynecologic Oncology Tumor Bank to examine the association of oncomorphic TP53 mutations with patient outcome using advanced serous ovarian cancer as a model. We demonstrate that oncomorphic TP53 mutations are associated with worse progression-free survival, chemoresistance, and higher rates of recurrence than other mutations in TP53 that have no evidence of oncomorphic abilities. We identify molecular alterations in patients with oncomorphic TP53 mutations, particularly the increased expression of β-catenin. We also observe that oncomorphic p53 proteins lose the normal protein:protein interactions with the microRNA microprocessing complex, implicating the role of dysregulated miRNAs in pathways associated with chemoresistance. The cumulative results from our studies provide human evidence for the consideration of different classes of TP53 mutations. Patients with oncomorphic TP53 mutations deserve careful follow-up therapy and may require novel treatment regimens to improve outcomes. We propose that stratification of patients should be considered based upon the individual TP53 mutation identified from their tumors.